1. Field of the Invention
The present invention relates to a semiconductor device, more particularly a ceramic-type semiconductor package provided with a metal cap depressed at the central portion thereof, and a process for producing the same.
2. Description of the Related Art
Conventional ceramic-type semiconductor packages generally include as main constituents a semiconductor pellet, a ceramic lead base having a cavity for accommodating the semiconductor pellet, and a metal cap for sealing the cavity. In many cases, the metal cap is given a central depressed portion shaped to correspond to the cavity so as to facilitate alignment.
The metal cap is produced by pressing a flat metal plate between a male die and a female die. The metal cap is seam-welded with a sealing metal frame bonded on a ceramic layer of the ceramic lead base by bringing electrodes into contact at opposite peripheral edge of flat portions of the metal cap. In conventional packages, however, the central depressed portion of the metal cap has a flat bottom surface. Mechanical stress due to the pressing concentrates at the angle portions. As a result, the flat bottom surface of the central depressed portion tends to bend in order to compensate for the residual stress. With such a bent metal cap, the electrodes for the seam weld contact the peripheral flat portions of the metal cap over a broad area, which leads to insufficient generation of heat and thus substandard seam-welding. Furthermore, the flat portion of the metal cap contacts the sealing metal frame on the ceramic layer only at a small area, so that insufficient seam-welding is obtained.